I've seen people lose weight on keto diet. My question is it safe? What is this doing to the muscle I've built? To my hormones as a woman? To my brain?

Keto works for weight loss, just like every other diet. The only thing that leads to weight loss is being on a deficit. Keto isn't sustainable, it might lead to weight loss and muscle loss as well.

Last year, I had surgery for cancer of the throat. My surgery has healed and I’ve completed a series of radiation treatments. Since then I have had a very dry taste in my mouth that I don’t seem to get rid of. Can you suggest some foods that are moist or a diet that would help me?

Opt for soft diet; foods like cooked oats, smoothies, milk etc.

What diet should I follow to gain weight without affecting my cholesterol?

Firstly, follow a calorie surplus diet. And choose healthy fats over all unhealthy unsaturated fats.

I have twin girls who are five years old. Ever since they started school it seems as if they are always kind of sick. In any given week they could each have a gross cough, runny nose, upset stomachs, and headaches. They eat fairly healthy for kids (they prefer fruits and veggies over candy and sugary foods). Are there any supplements, vitamins or superfood I could give them to help boost their immune systems?

They might have a weak immune system. If they're eating healthy then make sure they have an active lifestyle too.

My almost 3-year-old son won’t eat anything unless I give him chocolate. I do give him very small amount of chocolate to lure him into eating food but I’m worried that too much chocolate will have a negative impact on his health. Is there any healthy yet sweet alternative for chocolate that would make him think he’s still eating chocolate?

Sounds like he likes sweets a lot. Give him fruit smoothies, juices, dates sort of foods. Try and experiment with different recipes.